Recent international negotiations and domestic policy developments have generated interest in current and projected U.S. greenhouse gas (GHG) emission levels. GHG emissions are generated throughout the United States from millions of discrete sources. Of the GHG source categories, carbon dioxide (CO2) emissions from fossil fuel combustion account for the largest percentage (77%) of total U.S. GHG emissions. The electric power sector contributes the second largest percentage (35%) of CO2 emissions from fossil fuel combustion (one percentage point behind the transportation sector).